Apparatus for measuring hydraulic flow quantities and leaks in a specimen

ABSTRACT

An apparatus for measuring hydraulic flow quantities and leaks in a specimen, including a measuring section to which the specimen is coupled and a capacitive sensor disposed in the measuring section. The measuring section can be acted upon both by at least one measurement medium and by at least one pressure medium. For generating a pressure acting on the measurement medium an inlet/outlet for the measurement medium is embodied on a side of the measuring section remote from the specimen, and an inlet/outlet for the pressure medium is disposed directly on the measuring section, on a side of the measuring section toward the specimen.

PRIOR ART

The invention relates to an apparatus for measuring hydraulic flowquantities and leaks in a specimen, including a measuring section towhich the specimen is coupled and a capacitive sensor which is-disposedin the measuring section and is acted upon both by at least onemeasurement medium and by at least one medium (pressure medium) forgenerating a pressure acting on the measurement medium.

Such an apparatus is found for instance in German Patent Disclosure DE42 05 453 A1. In this apparatus, both the measurement medium and thepressure medium are delivered to the measuring section via separatesupply lines intended for them, indirectly via a compensation container.The inlet/outlet for the pressure medium and also for the measurementmedium are disposed on the compensation container; the inlet of thepressure medium cannot be closed by a valve, for instance. The specimencommunicates with the measuring section via a line. In such an apparatusit is problematic to measure a wide flow range. Furthermore, such anapparatus for measuring hydraulic flow quantities and leaks in specimenscannot be employed at very high pressures, since air is used as thepressure medium, which because of its compressibility necessitatesadherence to stringent safety requirements.

U.S. Pat. No. 5,017,909 discloses an apparatus for capacitive detectionof a liquid level that makes it possible to signal by means of a signallamp if the liquid in a container exceeds or drops below a particularlevel.

Measuring a pressure prevailing in a container by visual and opticalmeans using the liquid level of two liquids adjacent one another in acontainer is disclosed by U.S. Pat. No. 5,065,616.

Detecting a leak in a fluid system is also disclosed by U.S. Pat. No.5,152,167, in which a leak is detected via a liquid level found in thereservoir, but this level is not measured capacitively.

The object of the injection is to improve an apparatus for measuringhydraulic flow quantities and leaks in a specimen of this generic typein such a way that in a technologically achieved way, measurements withdifferent requirements are possible, such as measurements at highpressures or measurements over a wide flow range, and the like.

ADVANTAGES OF THE INVENTION

In an apparatus for measuring hydraulic flow quantities and leaks in aspecimen of the type described at the outset, this object is attainedaccording to the invention in that an inlet/outlet for the measurementmedium is embodied on a side of the measuring section remote from thespecimen, and an inlet/outlet for the pressure medium is disposeddirectly on the measuring section, on a side of the measuring sectiontoward the specimen.

Embodying the inlet/outlet for the measurement medium and theinlet/outlet for the pressure medium directly on the measuring sectionhas the particularly great advantage that both the measurement mediumand the pressure medium can be delivered to the measuring section andthus also to the specimen very quickly and without detours. Inparticular, by this provision the measuring section can be acted upondirectly by the measurement medium and the pressure medium. Thisarrangement allows a pressure in the measuring section and thus in thespecimen to be set precisely.

Advantageously, the inlet/outlet for the measurement medium and theinlet/outlet for the pressure medium can be shut off by valves.

An advantageous embodiment that in particular allows many differentmeasurement methods, provides that these valves are triggerable as afunction of pressure. In an exemplary embodiment in which a wide flowrange in particular is to be covered, it is provided that a compensationcontainer can be connected parallel to the measuring section.

In another advantageous embodiment, which can be used in particular forhydraulic flow quantities in the inflow at low pressure, a pressurereservoir that can be connected via a valve that is triggerable as afunction of pressure is disposed adjacent to the inlet/outlet for themeasurement medium on the measuring section.

Particularly for good coupling of the measurement medium, which is underpressure, to the specimen and for easy rinsing out of any air bubblesthat may arise, it is advantageously provided that a turbulizing elementfor generating a rotary flow in the specimen is disposed between theinflow (the high-pressure side) to the specimen and the measuringsection.

With regard to the embodiment of the turbulizing element, in principlethe most various forms that generate a rotary flow in the specimen areconceivable. One advantageous embodiment provides that the turbulizingelement is a cylindrical disk, with openings disposed in inclinedfashion in the axial and azimuthal directions. Such a turbulizingelement is on the one hand especially easy to manufacture and on theother hand generates especially effective rotary flows in the specimen.

Thus far no detailed information has been provided herein on theembodiment of the measuring section or of the capacitive sensor. Oneadvantageous embodiment provides that the measuring section takes theform of a cylinder, and that the capacitive sensor is a cylindercapacitor. In this way, the capacitive sensor, which is disposed as acylinder capacitor in the measuring section embodied as a cylinder, canbe acted upon in an especially simple way by the measurement medium andthe pressure medium, since in a sense the measuring section and thecapacitive sensor coincide.

Purely in principle, the most various fluids can be used as both themeasurement medium and the pressure medium. In one advantageousembodiment, it is provided that the measurement medium is a hydraulicfluid, and that the pressure medium is air.

In another advantageous embodiment, it is provided that the measurementmedium and the pressure medium are two liquids not miscible with oneanother, which have different dielectric constants and densities. If thehydraulic fluid has significant electrical conductivity, thenadvantageously one of the electrodes that form the capacitive sensor isprovided with a thin, homogeneous electrically insulating coating.

If the capacitive sensor is a tubular capacitor, then preferably thecenter conductor is provided with the insulating coating.

To allow decoupling from the measuring section, it may be provided inone embodiment that a shutoff valve is disposed between the specimen andthe measuring section.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention the subject ofthe ensuing description and of the drawings that show several exemplaryembodiments.

Shown in the drawings are:

FIG. 1, a first exemplary embodiment of an apparatus according to theinvention for measuring hydraulic flow quantities and leaks in aspecimen;

FIG. 2, a second exemplary embodiment of an apparatus according to theinvention for measuring hydraulic flow quantities and leaks in aspecimen;

FIG. 3, a third exemplary embodiment of an apparatus according to theinvention for measuring hydraulic flow quantities and leaks in aspecimen;

FIG. 4, a fourth exemplary embodiment of an apparatus according to theinvention for measuring hydraulic flow quantities and leaks in aspecimen;

FIG. 5, another coupling of the specimen to the measuring section, inthe exemplary embodiment shown in FIG. 4 of an apparatus according tothe invention for measuring hydraulic flow quantities and leaks in aspecimen;

FIG. 6, a further coupling of the specimen to the measuring section, inthe exemplary embodiment shown in FIG. 4 of an apparatus according tothe invention for measuring hydraulic flow quantities and leaks in aspecimen; and

FIG. 7, a basic circuit diagram of an evaluation circuit, which can beused in the apparatuses of the invention, shown in FIGS. 1-6, formeasuring hydraulic flow quantities and leaks.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

An exemplary embodiment of an apparatus for measuring hydraulic flowquantities and leaks in a specimen 10, such as an injection valve usedin automotive engineering, and shown in FIG. 1, includes a measuringsection 20, which extends approximately vertically and to whose lowerend the specimen 10 is coupled. In the measuring section 20 is acapacitive sensor 30 in the form of a cylinder capacitor, whose outercylinder 31 coincides with the outer tube of the measuring section 20and whose center conductor 33 is disposed essentially centrally in theouter cylinder 31 and thus the outer tube of the measuring section 20.

The specimen 10 is coupled to the measuring section 20 directly via asealing element 12.

An electrically insulated, perforated center conductor fastener 35 isprovided on the side of the capacitive sensor 30 toward the specimen 10.

On the side of the capacitive sensor 30 remote from the specimen 10, thecenter conductor 33 is extended to the outside, to an evaluation circuitto be explained in further detail below, via an electrically insulated,pressure-tight leadthrough 36.

On the side of the measuring section 20 toward the specimen 10, aninlet/outlet 40 for a measurement medium 50 is provided, by way of whichthe measuring section 20 and thus the capacitive sensor 30 in the formof the cylinder capacitor can be acted upon by the measurement medium50.

If the hydraulic measurement medium 50 is electrically conductive, thenthe center conductor 33 is provided with a thin, homogeneouselectrically insulating coating 34.

The inlet/outlet 40 of the measurement medium 50 can be closed via avalve 41 that is triggerable as a function of pressure.

Also on the side of the measuring section 20 remote from the specimen10, an inlet/outlet 60 is provided, by way of which a medium forgenerating a pressure, that is, a pressure medium 70, acting on themeasurement medium 50 can be delivered into the measuring section 20.The inlet/outlet 60 for the pressure medium 70 is closable via a valve61 that can be triggered as a function of pressure. Downstream of thevalve 61 is a manometer 64, which detects the pressure prevailing in themeasuring section 20.

Also on the side of the measuring section 20 remote from the specimen10, a relief/return valve 42 is provided, which in the open state allowsexcess measurement medium 50 to be removed from the measuring section 20via a line 45.

A turbulizing element 80 for generating a rotary flow in the specimen 10is also disposed between the specimen 10 and the measuring section 20and thus the capacitive sensor 30. As a result of this rotary flow,bubbles or the like in particular, which can arise on impingement of themeasurement medium 50 on the specimen 10, are flushed out of themeasurement medium 50 and the specimen 10. To that end, the specimen 10is briefly opened, via the electric trigger line 11. The turbulizingelement takes the form of a cylindrical disk with openings (not shown)inclined in the axial and azimuthal directions.

In the apparatus shown in FIG. 1, which is suitable in particular forflow measurement in the low-pressure range (2 to 10 bar), a hydraulicfluid 50 is preferably used as the measurement medium 70, and air ispreferably used as the pressure medium. The center conductor 33 has adiameter of approximately 0.5 mm, while the outer cylinder 30 converselyhas a diameter of approximately 2 mm. Prior to the measurement, themeasuring section 20 is filled. For measurement, the valves 41, 42 areclosed while the valve 61 in the inlet/outlet 60 of the pressure medium70 is opened. In this way, the measuring section 20 is acted upon by atest pressure p, which is detected by the manometer 64. The specimen 10is now opened under the control of a control line 11, and the level ofmeasurement medium 50 is detected by the capacitive sensor 30 andcarried on to an evaluation circuit to be described in further detailhereinafter.

The level in the measuring section 20 and thus in the capacitive sensor30 in the form of the cylinder capacitor is a measure for the flowquantity or for a leak in the specimen 10.

In a second exemplary embodiment, shown in FIG. 2, those elements thatare identical to elements in the first exemplary embodiment are providedwith the same reference numerals so that with regard to theirdescription, reference is made to the full content of the description ofthe first exemplary embodiment. The exemplary embodiment shown in FIG. 2of an apparatus for measuring hydraulic flow quantities and leaksdiffers from that shown in FIG. 1 in that a compensation or supplycontainer 81 can be connected parallel to the measuring section 20, viavalves 43, 63.

In addition, a shutoff valve 22 is disposed between the measuringsection 20 and where the specimen 10 is coupled to the measuring section20, or in other words between the sealing element 12 and turbulizingelement 80 and the end of the measuring section 20 toward the specimen.This apparatus is intended for measurement of flow and tightness in theinflow, that is, the high-pressure side, of a specimen 10 to be actedupon by high pressure, such as a high-pressure injection valve; testpressures between 100 and 250 bar are contemplated.

This apparatus is especially advantageous whenever a wide flow range isto be covered. In that case, the supply container is connected to themeasuring sensor; that is, the valves 43, 63 are open during themeasurement. Furthermore, this apparatus is used particularly when largeflushing quantities are to be furnished. Once again, during theflushing, the compensation and supply container 81 is connected parallelto the measuring sensor 20.

The apparatus also makes it possible to perform measurement with anenclosed gas volume. During the measurement, all the valves except forthe valve 43 are closed. In this way, a defined gas volume develops inthe upper region of the measuring sensor 20, acted upon by the pressuremedium 70, and also in the upper region of the compensation and supplycontainer that is acted upon by the pressure medium 70. This gas volumecan be compressed by delivering the medium via opened valves 61, 63.This compression creates a pressure p above the measurement medium 50that can be employed for measuring the specimen 10. During themeasurement, with the valve 63 closed, measurement medium 50 can bedelivered to the compensation and supply container via the opened valve61 as a function of the pressure p detected by the manometer 64. Afterclosure of the valve 61 and opening of the valve 63, the level ofmeasurement medium 50 in the measuring section 30 is equalized on theprinciple of communicating tubes. The above-described measuring methodis particularly advantageous when the measuring pressures are very high,since the gas volume is preserved unchanged. Filling the apparatus canbe done at low pressure on the part of the pressure medium 70, if theapparatus is first filled entirely with the pressure medium 70, that is,a gas, and the valve 41 is then closed and the high pressure generationis done by delivering measurement medium 50 through the open valves 61,63. In this apparatus as well, the measuring section 20 can be filledvery rapidly.

In a third exemplary embodiment, shown in FIG. 3, those elementsidentical to elements in the first embodiment are provided with the samereference numerals, so that with regard to their description, referenceis made to the full content of the description of the first exemplaryembodiment.

The exemplary embodiment shown in FIG. 3 differs from that shown in FIG.1 in that instead of a return valve disposed on the side of themeasuring section 20 remote from the specimen 10, a pressure reservoir90 is provided, which can be connected to the measuring section 20 via avalve 91 that is triggerable as a function of pressure.

This apparatus is used particularly for hydraulic flow quantities in theinflow to the specimen 10 at low pressure, that is, at a test pressureof 2 to 10 bar. The control of the valves 61, 41 and 91 is dependent onthe pressure p detected by the manometer 64, in such a way thatmeasurement medium 50 never reaches the uppermost region of themeasuring section 20. The apparatus allows a low pressure of thepressure medium 70, for instance if gas is used as the pressure medium70, such as a low pneumatic pressure, to be compressed by means of ahigher pressure of the measurement medium 50 into the pressure reservoir90. The column of measurement medium 50 here acts as a piston.

An especially advantageous feature of this apparatus is that only aslight quantity of gas is lost per measurement cycle, since the valve 91is closed after the measurement. Using this apparatus is moreoveradvantageous whenever a pressure supply, such as a pneumatic supply, forgenerating the pressure prevailing in the pressure medium 70 does notfunction in stable fashion.

Furthermore, by means of this apparatus a higher pressure of thepressure medium 70 can easily be generated with the aid of themeasurement medium 50.

In the apparatuses shown in FIGS. 1-3, a hydraulic fluid is used as themeasurement medium 50, while a gas is conversely used as the pressuremedium 70.

However, an apparatus for measuring hydraulic flow quantities and leaksis also conceivable in which the measurement medium 50 and the pressuremedium 70 are two conductive liquids, such as hydraulic liquids, thatare immiscible with one another. One exemplary embodiment of such anarrangement is shown in FIG. 4. The embodiment shown in FIG. 4 differsfrom that shown in FIG. 1 in that instead of a gaseous or in other wordscompressible pressure medium 70, a noncompressible liquid pressuremedium 71 is used, which has a higher density than the measurementmedium 50. The latter is delivered as described above, on the side ofthe measuring section 20 remote from the specimen 10, via theinlet/outlet 60 with the aid of the pressure-dependently triggerablevalve 61. At approximately the same height along the measuring section20, a pressure equalization vessel 72 that can be connected to a valve73 is also provided; it is at least partly filled with the pressuremedium 71. The specimen 10 can be decoupled from the measuring section20 via a shutoff valve 22.

In the event that one of the two hydraulic measurement mediums 50, 71has significant electrical conductivity, the center conductor 33 isprovided with a thin, homogeneous electrically insulating coating 34.

The advantage of this apparatus is that it can be used up to extremelyhigh pressures (on the order of magnitude of 1000 bar). This apparatusis especially advantageous whenever, for instance for safety reasons, agaseous pressure medium 70 cannot be used, or a gaseous pressure medium70 is soluble in the measurement medium 50 at high pressures. Testingthe specimen 10 for tightness or measurement of a flow quantity is donein the manner described in conjunction with the first exemplaryembodiment (FIG. 1).

The embodiment shown in FIG. 5 differs from that in FIG. 4 only in thatthe specimen "spurts out" not at the top but at the bottom, bydeflection by 180°.

The embodiment shown in FIG. 6 differs from that in FIG. 5 in that thepressure medium 71 has a lesser density than the measurement medium 50.Those elements identical to elements of the exemplary embodiment shownin FIG. 5 are provided with the same reference numerals, so that withregard to their description, reference is made to the full content ofthe description of the first exemplary embodiment.

The measurement of the capacitance of the capacitive sensor 30 disposedin the measuring section 20 is done as schematically shown in FIG. 7.The capacitive sensor Cx, together with positive and regenerativefeedback resistances Rf, Rm1, Rm2, is the frequency-determining elementof a measurement oscillator (square wave generator) known per se. Theresultant period length T of the oscillator is directly proportional toCx. With a capacitance Cx of approximately 20 pF, a positive feedbackresistance Rf=5 MQ and regenerative feedback resistances Rm1, Rm2=230kΩ, T for instance becomes 230 μs, or in other words an oscillatorfrequency F of approximately 4.3 kHz. The measurement oscillator signal,corresponding to the sensor capacitance, is delivered to two counterchains, which each include one counter 1 and one counter 2; the signaldelivered to the counter 2 is inverted. Each of the counter chains ispreceded by a respective NAND gate 100 with two inputs. To one of thetwo inputs of each NAND gate, a common 100 MHz signal of a referenceoscillator is applied; this signal is generated via a quartz oscillatorcomponent, known per se. The NAND gate of the counter 1 allows this 100MHz frequency to pass through it during the time while the output of themeasurement oscillator is at HIGH. Since the measurement oscillatorsignal used for the counter 2 is inverted, the NAND gate of the counter2 allows the 100 MHz signal to pass through it during the LOW phase ofthe measurement oscillator signal.

The counters 1, 2 of the two counter chains are each 16-bit counters. Amicrocontroller reads out the counter states in succession.

A difference is ascertained from the readout in a preceding measurementoscillator period. This difference tells the length of the respectivehalf (HIGH/LOW) of the measurement oscillator period in 10 ns units(with a reference frequency of 100 MHz). Adding the respectively other,previously measured half-period, after measurement of each half-period,yields the instantaneous total measurement oscillator period T in 10 nsunits. For the aforementioned time constant T=230 μs, a period ofapproximately 23,000 thus results.

By this type of period of inter-nested readout of the counter chains,very high chronological resolution is obtained (typically approximately120 μs). In this way, very fast measurements are possible.

For the measurement, a predetermined number of measured values areprocessed in a test bench computer (not shown). By means of thepreselectable number of such measurements, a compensation curve with aconstant term that fades in proportion to time and exponentially isdrawn in accordance with the following formula:

    Measured value=constant+leakiness*t+K*exp(-t/to).

The exponentially fading term takes into account the effects producedparticularly from trapped air in the specimen 10 (adiabatic heating onimposition of the flushing/test pressure and ensuing volumetricreduction from cooling). The time constant to is dependent essentiallyonly on the specimen 10 used, which for instance belongs to a family ofinjection valves, and can therefore be determined with general validitybeforehand. The variable K is a measure for the volume of the trappedair and can be monitored.

For slow measurements, typically eighty (80) measurement oscillatorperiods per measured value detection are read out. On averaging over thelast ten measurements at intervals typically of 50 to 200 μs, a measuredvalue of approximately 18,000,000 is obtained for a well-filled sensor.For an empty sensor, the measured value is approximately 15,000,000.Thus the fill extent of the sensor can also be detected; that is,disruptions in the supply of the measurement medium 50, a large leak ofthe specimen 10, excessively high amounts of trapped air, and so forthcan be detected.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. An apparatus for measuring hydraulic flow quantities andleaks in a specimen (10), comprising a measuring section (20) to whichthe specimen (10) is coupled and a capacitive sensor (30) disposed inthe measuring section (20), said measuring section (20) is acted uponboth by at least one measurement medium (50) and by at least onepressure medium (70) for generating a pressure acting on the measurementmedium (50), an inlet/outlet (60) for the pressure medium (70) isdisposed directly on the measuring section (20), on a side of themeasuring section (20) remote from the specimen (10), and a turbulizingelement (80) for generating a rotary flow in the specimen (10) isdisposed between the inflow to the specimen (10) and the measuringsection (20).
 2. An apparatus for measuring hydraulic flow quantitiesand leaks in a specimen (10), comprising a measuring section (20) towhich the specimen (10) is coupled and a capacitive sensor (30) disposedin the measuring section (20), said measuring section (20) is acted uponboth at least one measurement medium (50) and by at least one pressuremedium (70) for generating a pressure acting on the measurement medium(50), an inlet/outlet (40) for the measurement medium (50) is embodiedon a side of the measuring section (20) toward the specimen (10), and aninlet/outlet (60) for the pressure medium (70) is disposed directly onthe measuring section (20), on a side of the measuring section (20)remote from the specimen (10), and said capacitive sensor (30) isprovided with a center conductor (33) that includes an electricallyinsulating coating (34).
 3. The apparatus according to claim 2, in thatthe inlet/outlet (40) for the measurement medium (50) and theinlet/outlet (60) for the pressure medium (70) can be shut off by firstand second triggerable valves (41, 61).
 4. The apparatus according toclaim 3, in that the first and second triggerable valves (41, 61) aretriggerable as a function of pressure.
 5. The apparatus according toclaim 3, in that a compensation and supply container (81) is connectedin parallel with the measuring section (20).
 6. The apparatus accordingto claim 3, in that a compensation and supply container (81) isconnected in parallel with the measuring section (20).
 7. The apparatusaccording to claim 2, in that a pressure reservoir (90) is connected viaa valve (91) that is triggerable as a function of pressure is disposedadjacent to the inlet/outlet (40) for the measurement medium (50) on themeasuring section (20).
 8. The apparatus according to claim 3, in that apressure reservoir (90) is connected via a valve (91) that istriggerable as a function of pressure is disposed adjacent to theinlet/outlet (40) for the measurement medium (50) on the measuringsection (20).
 9. The apparatus according to claim 1, in that theturbulizing element (80) is a cylindrical disk, with openings disposedin inclined fashion in the axial and azimuthal directions.
 10. Theapparatus according to claim 2, in that the measurement medium (50) is ahydraulic fluid, and that the pressure medium (70) is air.
 11. Theapparatus according to claim 2, in that the measurement medium (50) andthe pressure medium (71) are two liquids not miscible with one another,which have different dielectric constants and densities.
 12. Theapparatus according to claim 2, in that a shutoff valve (22) is disposedbetween the specimen (10) and the measuring section (20).
 13. Anapparatus for measuring hydraulic flow quantities and leaks in aspecimen (10), comprising a measuring section (20) to which the specimen(10) is coupled and a capacitive sensor (30) disposed in the measuringsection (20), said measuring section (20) is acted upon both by at leastone measurement medium (50) and by at least one pressure medium (70) forgenerating a pressure acting on the measurement medium (50), aninlet/outlet (40) for the measurement medium (50) is embodied on a sideof the measuring section (20) toward the specimen (10), and aninlet/outlet (60) for the pressure medium (70) is disposed directly onthe measuring section (20), on a side of the measuring section (20)remote from the specimen (10), and the measuring section (20) takes theform of a cylinder, and that the capacitive sensor (30) is a cylindercapacitor.